Article pubs.acs.org/IECR
Nitrogen-Doped Porous Carbon Spheres Derived from Polyacrylamide Xiang Ying Chen,*,† Chong Chen,† Zhong Jie Zhang,‡ and Dong Hua Xie† †
School of Chemical Engineering, Anhui Key Laboratory of Controllable Chemistry Reaction & Material Chemical Engineering, Hefei University of Technology, Hefei, Anhui 230009, P. R. China ‡ College of Chemistry & Chemical Engineering, Anhui Province Key Laboratory of Environment-friendly Polymer Materials, Anhui University, Hefei 230039, Anhui, P. R. China S Supporting Information *
ABSTRACT: Spherical nitrogen-doped porous carbons have been prepared through a template carbonization method, in which polyacrylamide (PAM) serves as carbon and nitrogen sources, and calcium acetate as hard template. It reveals that the mass ratio of polyacrylamide and calcium acetate and the carbonization temperature have crucial impacts upon the pore structures and the correlative capacitive performance. The PAM-Ca-650-1:3 sample displays the best capacitance performance. It is amorphous with low-graphitization degree, possessing a total BET surface area of 648 m2 g−1 and total pore volume of 0.59 cm3 g−1. At a current density of 0.5 A g−1, the resultant specific capacitance is 194.7 F g−1. It exhibits high capacitance retention of 97.8% after charging−discharging 5000 times. The polyacrylamide used is cheap and commercially available, making it promising for largescale production of porous carbons containing nitrogen as an excellent electrode material for supercapacitor. Polyacrylamide is a polymer (−CH2CHCONH2−) formed from acrylamide subunits. It is highly water-absorbent, forming a soft gel when hydrated and can be used in such applications as polyacrylamide gel electrophoresis and in manufacturing soft contact lenses. In virtue of the high contents of carbon and nitrogen elements, PAM is expected to be an excellent candidate for producing porous carbons doped with nitrogen. Thus far, as much as we know, few studies concerning the preparation of carbons, in particular spherical ones, derived from PAM have been documented.19,20 Herein, we demonstrate a template carbonization method to prepare porous carbons containing nitrogen, using PAM as carbon/nitrogen sources and calcium acetate as hard template. Several reaction parameters such as the mass ratio of PAM and calcium acetate and carbonization temperature were investigated in depth, primarily based on the correlative capacitive performances by cyclic voltammetry and galvanostatic charge− discharge techniques.
1. INTRODUCTION Nitrogen-doped porous carbon materials, from the viewpoint of practical application, have proved to be intriguing candidates for supercapacitors.1 On the one hand, porous carbons can provide high surface area, high pore volume, and proper pore structure and pore size distribution for electrolyte diffusion.2,3 On the other hand, incorporating nitrogen into porous carbons can enhance the capacitance incurred by the pseudo-capacitive effect and strengthen the wettability of the interface between electrolyte and electrode. Also, the nitrogen functionalities are capable of inducing electron-donor properties.4 Therefore, nitrogen-doped porous carbon materials could probably fulfill one of the most critical requirements, to enhance their energy density while retaining their intrinsic high specific power, in the development of supercapacitors.5 Currently, the template carbonization method is a convincing protocol for producing porous carbon materials with precisely controlled structures.6 Two types of templates, classified as a soft template or hard template, are commonly used as scaffolds to pave the way for the formation of pores during the carbonization process. Among them, hard templates can possess inherited porosity and are usually infiltrated with carbon precursor, followed by carbonization and etching of the template.7 Different types of hard templates have been brought forward so far, such as Ni(OH)2,8 MgO,9,10 anodized aluminum oxide,11 natural sepiolite,12 silica,13,14 and zeolite.15 Next, to further improve the electrochemical performance of supercapacitors, a certain amount of nitrogen is generally incorporated into porous carbons mainly through the following two strategies, including in situ doping by carbonization of nitrogen-rich precursors, polyacrylonitrile,16 biomass,17,18 and post-treatment of carbons with gaseous NH3.1 However, design and synthesis of porous carbons especially with well-defined characteristics remains a big challenge. © 2013 American Chemical Society
2. EXPERIMENTAL SECTION All analytical chemicals were purchased from Sinopharm Chemical Reagent (Shanghai) Co. Ltd. and used as received without further treatment. 2.1. Typical Synthetic Procedure for the PAM-Ca-6501:3 Sample. PAM and Ca(OAc)2·H2O with designated mass ratio of 1:3 were dissolved in deionized water to form a clear solution, respectively, which were further mixed together to form a white suspension under constant magnetic stirring. After being heated at 110 °C for 5 h in an electric oven, white Received: Revised: Accepted: Published: 12025
May 29, 2013 July 14, 2013 July 30, 2013 July 30, 2013 dx.doi.org/10.1021/ie4017013 | Ind. Eng. Chem. Res. 2013, 52, 12025−12031
Industrial & Engineering Chemistry Research
Article
Figure 1. PAM-Ca-650-1:3 sample: (a) XRD pattern; (b) FESEM; and (c−d) HRTEM images. The inset of part d is the SAED pattern. (e) N2 adsorption−desorption isotherm. (f) Cumulative pore volume and pore-size distribution curves (calculated by using a slit/cylindrical NLDFT model).
powder was obtained. Next, the powder freshly prepared was placed in a porcelain boat, flushed with Ar flow for 30 min, and heated in a horizontal tube furnace up to 650 °C at a rate of 5 °C min−1 and maintained at this temperature for 2 h under Ar flow. The resultant product was immersed with dilute HCl solution to remove soluble/insoluble substances, which was further washed with adequate deionized water until pH = 7. Finally, the sample was dried under vacuum at 120 °C for 12 h to obtain the PAM-Ca-650-1:3 sample. For comparison, we also prepared a series of carbon samples by altering the carbonization temperature, and the mass ratio of PAM and Ca(OAc)2·H2O, called PAM-600, PAM-Ca-600-1:1, PAM-Ca-600-1:3, PAM-Ca-600-1:5, and PAM-Ca-700-1:3. Note that the PAM-Ca-650-1:3 sample displays the best capacitive performance among these carbon samples, thus it was emphatically investigated in present work. 2.2. Characterization. X-ray diffraction (XRD) patterns were obtained on a Rigaku D/MAX2500 V with Cu Kα radiation. Field emission scanning electron microscopy
(FESEM) images were taken with a Hitachi S-4800 scanning electron microscope. High-resolution transmission electron microscope (HRTEM) images and selected area electron diffraction (SAED) pattern were performed with a JEM-2100F operated at 200 kV. X-ray photoelectron spectra (XPS) were obtained on a VG ESCALAB MK II X-ray photoelectron spectrometer with an exciting source of Mg Kα (1253.6 eV). The specific surface area and pore structure of the carbon samples were determined by N2 adsorption−desorption isotherms at 77 K (Quantachrome Autosorb-iQ) after being vacuum-dried at 150 °C overnight. The specific surface areas were calculated by the BET (Brunauer−Emmett−Teller) method. Cumulative pore volume and pore-size distribution were calculated by using a slit/cylindrical nonlocal density functional theory (NLDFT) model. The micropore areas and external surface areas were calculated by t-plot. 2.3. Electrochemical Measurements. In order to evaluate the capacitive performances of the as-prepared carbon samples (∼4 mg) in electrochemical capacitors, a mixture of 80 wt % of 12026
dx.doi.org/10.1021/ie4017013 | Ind. Eng. Chem. Res. 2013, 52, 12025−12031
Industrial & Engineering Chemistry Research
Article
HRTEM image taken from the wall of one hollow sphere is shown in Figure 1d. The lattice fringes are very vague, and the corresponding SAED pattern in the inset of Figure 1d also displays faint diffraction rings, all of which apparently suggest the amorphous nature of the PAM-Ca-650-1:3 sample. On the other hand, the typical FESEM images of PAM-Ca-600-1:3 and PAM-Ca-700-1:3 samples are shown in Supporting Information Figure S1. In detail, the former mainly consists of irregular carbon sheets; whereas, the latter is made up of large numbers of spheres with open or sealed surfaces. It is thus concluded that the carbonization temperature is crucial for the formation of well-defined hollow carbon spheres under present circumstances. As for the present formation mechanism for producing porous carbon spheres, the calcium acetate involved is certainly indispensable. As was well-reported, calcium acetate can be transformed into CaCO3 at the temperature of 300−500 °C and the newly produced CaCO3 further decompose into CaO at 600−1000 °C.21 Of course, the newly formed acetone from the decomposition of calcium acetate can also play a partial role in the formation of porous structure of final carbon sample. Therefore, in case of the PAM-Ca-650-1:3 sample, the solid remains after carbonizing a mixture of PAM and calcium acetate (mass ratio of 1:3) at 650 °C are probably CaCO3 and/or CaO. This calcium carbonate/oxide can actually work as hard templates, which were further removed from the product by adequate treatment with dilute HCl solution and deionized water. By all appearances, the templating role of present calcium acetate for hollow spheres is to some extent analogous to those of magnesium acetate,19 silica,22 and CaCO3.23 Brunauer−Emmett−Teller (BET) surface area and pore structure of the PAM-Ca-650-1:3 sample were investigated by N2 adsorption−desorption isotherm, and pore size distribution was calculated by using a slit/cylindrical nonlocal density functional theory (NLDFT) model. It supposes a slit pore geometry for micropores and cylindrical pore geometry for mesopores. As a result, the total BET surface area is 648 m2 g−1 and total pore volume is 0.59 cm3 g−1. Furthermore, based on the calculation of t-plot, the micropore surface area is 91 m2 g−1 (i.e., the external surface area as 557 m2 g−1) and the micropore volume is 0.11 cm3 g−1 (i.e., the external pore volume as 0.48 cm3 g−1). Figure 1e shows the typical N2 adsorption−desorption isotherm of the PAM-Ca-650-1:3 sample, exhibiting type IV according to IUPAC classification. It also reveals the coexistence of multiple pore sizes ranging from micropores to macropores.24 The small amount of nitrogen adsorption at the initial stage indicates the low content of microporosity in the carbon sample. And most of the nitrogen adsorption occurs within meso-/macro-pores. This trend complies well with the BET and pore volume values, as is listed above. Besides, cumulative pore volume and pore-size distribution curves (calculated by using a slit/cylindrical NLDFT model) are demonstrated in Figure 1f. We can clearly see that the most probable distribution existing with the PAM-Ca-650-1:3 sample is of 0.5−10 nm, with two maximum pore widths of 1.4 and 4.9 nm, which is somewhat consistent with the reported value for average pore width (3.3 nm). The quantitative composition and content analysis of the PAM-Ca-650-1:3 sample was detected by an XPS technique, and the resultant peaks are fitted by XPS peak software. Furthermore, the contents of different peaks are approximately calculated, as shown in the inset of Figure 2. The survey
the carbon sample, 15 wt % acetylene black, and 5 wt % polytetrafluoroethylene (PTFE) binder was fabricated using ethanol as a solvent. A slurry of the above mixture was subsequently pressed onto nickel foam under a pressure of 20 MPa, serving as the current collector. The prepared electrode was placed in a vacuum drying oven at 120 °C for 24 h. A three electrode experimental setup taking a 6.0 mol L−1 KOH aqueous solution as electrolyte was used in cyclic voltammetry and galvanostatic charge−discharge measurements on an electrochemical working station (CHI660D, ChenHua Instruments Co. Ltd., Shanghai). Here, the prepared electrode, platinum foil (6 cm2) and saturated calomel electrode (SCE) were used as the working, counter, and reference electrodes, respectively. Specific capacitances derived from galvanostatic tests can be calculated from the equation:
C=
I Δt mΔV
where C (F g−1) is the specific capacitance; I (A) is the discharge current; Δt (s) is the discharge time; ΔV (V) is the potential window; and m (mg) is the mass of active materials loaded in working electrode. Specific capacitances derived from cyclic voltammetry tests can be calculated from the equation: C=
1 mv(Vb − Va)
∫V
Vb
I dV
a
where C (F g−1) is the specific capacitance; m (mg) is the mass of active materials loaded in working electrode; v (V s−1) is the scan rate; I (A) is the discharge current; Vb and Va (V) are high and low potential limit of the CV tests. Specific energy density (E) and specific power density (P) derived from galvanostatic tests can be calculated from the equations: 1 E = C ΔV 2 2 P=
E Δt
where E (W h kg−1) is the average energy density; C (F g−1) is the specific capacitance; ΔV (V) is the potential window; P (W kg−1) is the average power density; and Δt (s) is the discharge time.
3. RESULTS AND DISCUSSION The purity and crystallinity of the PAM-Ca-650-1:3 sample was studied by XRD pattern, as displayed in Figure 1a. No diffraction peaks assignable to calcium acetate, calcium carbonate, or calcium oxide appear, indicating the high purity of carbon product through the present washing procedure. The broad and low intensity peak centered at 23.1° reveals that the PAM-Ca-650-1:3 sample is amorphous with low-graphitization degree. The size and shape of the PAM-Ca-650-1:3 sample were characterized by FESEM and HRTEM techniques. The representative FESEM image shown in Figure 1b indicates that the carbon sample is mostly composed of spherical particles, with average diameter of ∼300 nm. And also, these carbon spheres authentically exhibit hollow structures, as revealed in Figure 1c. The intrinsic structure of carbon spheres was further detected by HRTEM technique, and the resulting 12027
dx.doi.org/10.1021/ie4017013 | Ind. Eng. Chem. Res. 2013, 52, 12025−12031
Industrial & Engineering Chemistry Research
Article
Figure 2. PAM-Ca-650-1:3 Sample: (a) XPS survey spectrum; (b) C1s; (c) N1s; (d) O1s.
Figure 3. PAM-Ca-650-1:3 sample: (a) CV curves at scan rates of 5−200 mV s−1; (b) specific capacitances calculated from CV curves; (c) galvanostatic charge−discharge curves measured at current densities of 0.5−20 A g−1; (d) specific capacitances calculated from discharge curves.
12028
dx.doi.org/10.1021/ie4017013 | Ind. Eng. Chem. Res. 2013, 52, 12025−12031
Industrial & Engineering Chemistry Research
Article
Figure 4. PAM-Ca-650-1:3 sample: (a) cycling durability within 5000 cycles at a current density of 20 A g−1; (b) galvanostatic charge−discharge curves of the 1st and 5000th cycles, as well as IR drop (the inset); (c) ragone plot showing energy density vs power density; (d) pristine Nyquist plots before/after 5000 cycles, as well as equivalent circuit modeling and the Nyquist plots fitted by Zview software (the inset).
in shape whereas high scan rates such as 50−200 mV s−1 can result in CV curves more deviating from rectangles. This arises from the fact that, compared with those at high scan rates, OH− ions at relatively low scan rates have much more time to transfer between the solution into the surface of electrode materials during the charging/discharging process.30 Besides, no obvious redox peaks appear in these CV curves, obviously indicating little contribution from redox reaction incurred by the dopant of nitrogen within carbon samples. On the other hand, the specific capacitances calculated from the CV curves in Figure 3a at scan rates of 5−200 mV s−1 are given in Figure 3b. It is seen that high specific capacitance of 290.3 F g−1 can be achieved at low scan rate of 5 mV s−1. Next, along with the increase of scan rates, the corresponding specific capacitances gradually decrease. Even at high scan rate of 200 mV s−1, the specific capacitance is 157.2 F g−1, whose capacitance retention is ca. 54.2% in contrast to that at scan rate of 5 mV s−1. It is also noteworthy that, according to the CV results shown in Supporting Information Figure S2, the PAM-Ca-650-1:3 sample displays the largest specific capacitances calculated from CV curves. Galvanostatic charge−discharge tests of the PAM-Ca-6501:3 sample were further carried out at different current densities of 0.5−20 A g−1 in 6.0 mol L−1 KOH aqueous solution, as shown in Figure 3c. All curves exhibit nearly symmetric triangular shapes in a potential range of −1.0−0.0 V, confirming excellent capacitive behaviors originating from electrical double-layer capacitor (EDLC). Additionally, we can see that the lower current density, the longer discharging time. Moreover, the PAM-Ca-650-1:3 sample has the largest discharging time among the present carbons, as illustrated in
spectrum with binding energies ranging from 0 to 1400.0 eV is indicated in Figure 2a. It solely consists of carbon, nitrogen, and oxygen elements without any other impurities, and their corresponding contents are of ca. 91.66%, 3.25%, and 5.09%, respectively. The high resolution C1s spectrum is shown in Figure 2b, and it can basically be fitted into four peaks in the range of 280.0−296.0 eV. The peak at ca. 284.6 eV is assignable to an sp2 CC bond, while the one at ca. 285.2 eV can be attributed to an sp3 CC bond of graphitic structure.25 In addition, the binding energies at ca. 286.4 and 289.3 eV represent the contributions from CO and OCO, respectively.26 Figure 2c reveals the high resolution spectrum of N1s with binding energies from 392.0 to 410.0 eV. On the whole, three individual peaks with different binding energies can be obtained with the help of XPS peak software. The peaks locating at ca. 398.5, 400.4, and 401.3 eV correspond to pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen, respectively.27,28 Regarding the high resolution spectrum of O1s, it primarily can be fitted into three peaks at binding energies of 525.0− 543.0 eV, as given in Figure 2d. In details, the peak at ca. 531.4 eV is due to isolated OH/CO/OCO, and the one at can be ascribed to ca. 532.6 eV CO/OCO. As for the one at ca. 533.6 eV, it comes from the contributions of C OC/COOH/COH.29 The cyclic voltammetry (CV) technique in a potential range of −1.0−0.0 V was first adopted to estimate the capacitive properties of the PAM-Ca-650-1:3 sample as the supercapacitor electrode. Figure 3a shows the CV curves at scan rates ranging from 5 to 200 mV s−1. Clearly, CV curves at low scan rates such as 5−20 mV s−1 are much closer to ideal rectangles 12029
dx.doi.org/10.1021/ie4017013 | Ind. Eng. Chem. Res. 2013, 52, 12025−12031
Industrial & Engineering Chemistry Research
Article
nitrogen sources and calcium acetate as a hard template. Several scientific merits involved in present work are as follows: (1) both the PAM and calcium acetate used are cheap and commercially available, making it possible for large-scale production of nitrogen-doped porous carbons; (2) without the help of any kind of activation process, the present template carbonization method is thus straightforward and reproducible; (3) spherical porous carbon can be achieved, in the case of the PAM-Ca-650-1:3 sample, simply by manipulating the mass ratio of PAM and calcium acetate, as well as the carbonization temperature; (4) the present carbon samples, especially the PAM-Ca-650-1:3 sample, display fairly good capacitive performances for potential application in supercapacitor.
Figure 3a and b. As a result, the specific capacitances calculated from discharge curves are demonstrated in Figure 3d. In the case of low current density of 0.5 A g−1, the specific capacitance is 194.7 F g−1. At high current densities of 20 and 40 A g−1, their specific capacitances are 90.0 and 62.0 F g−1, respectively, with the corresponding capacitance retentions of 46.2% and 31.8%. To sum up, based on the specific capacitance results shown in Supporting Information Figure S2f and Figure S3c, the rate capability of the PAM-Ca-650-1:3 sample is the highest and it can be utilized as superior electrode material for supercapacitors. Long cycling durability of supercapacitors is another crucial factor in determining practical application. The specific capacitance of the PAM-Ca-650-1:3 sample within 5000 cycles was measured at a current density of 20 A g−1 by a three electrode experimental setup, using 6 mol L−1 KOH aqueous solution as electrolyte, and the result is displayed in Figure 4a. Notably, it exhibits high capacitance retention of 97.8% even after charging−discharging for 5000 times. The present longterm electrochemical stability can be further evinced by the first and 5000th cycles of galvanostatic charge−discharge tests, as depicted in Figure 4b. Especially, the IR drops (i.e., potential drops) of the first and 5000th cycles are nearly equal, revealing that the overall internal resistances of the electrodes used almost stay invariable during the cycling process.31 Specific energy density (E) and specific power density (P) of the PAM-Ca-650-1:3 sample derived from galvanostatic tests are calculated and shown in Figure 4c. When power densities increase from 0.25 kW kg−1 to 20.0 kW kg−1, energy densities accordingly decrease from 27.0 W h kg−1 to 8.6 W h kg−1. Taking as an example, when designating power density as 10.0 kW kg−1, the corresponding energy density can reach up to 12.5 W h kg−1, indicating that the present carbon can provide a high energy density without sacrificing power density.32 Figure 4d shows the Nyquist plots before/after 5000 cycles of the PAM-Ca-650-1:3 sample. In a Nyquist plot, the imaginary part of the impedance is plotted as a function of the real part, often represented as follows: Z=
■
ASSOCIATED CONTENT
■
AUTHOR INFORMATION
S Supporting Information *
FESEM images; CV curves at scan rates of 5−100 mV s−1; specific capacitances calculated from CV curves; galvanostatic charge−discharge curves measured at current densities of 0.5− 1.0 A g−1; specific capacitances calculated from discharge curves; Ragone plots; overall resistance (Rt), electrical connection resistance (Re), electrolyte resistance (Rs), and resistance of ion migration in carbon micropores (Rp) of the carbon samples; capacitive performance conducted in a twoelectrode system using KOH as electrolyte; schematic illustration of a supercapacitor cell. These materials are available free of charge via the Internet at http://pubs.acs.org.
Corresponding Author
*Tel./Fax: +86-551-2901450. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21101052) and China Postdoctoral Science Foundation (20100480045). Z.J.Z. also thanks the Anhui Province Key Laboratory of Environmentfriendly Polymer Materials, Anhui University, Hefei 230039, China (KF2012009), for financial support.
E = Z0 exp(jϕ) = Z0(cos ϕ + j sin ϕ) I
As far as an ideal capacitor EDLC is concerned, Nyquist plots take on vertical lines with the real part of Z being 0.33 In present work, the two plots in Figure 4d are almost vertical in the frequency range of 100 kHz to 0.01 Hz, indicating the approximately ideal feature of EDLC for the PAM-Ca-650-1:3 sample. These pristine Nyquist plots before/after 5000 cycles were further fitted by ZView software with the help of equivalent circuit modeling, as depicted in the inset of Figure 4d. Each Nyquist plot consists of a depressed semicircle in the high frequency region and a straight Warburg line in the low frequency region. Note that the two semicircles before/after 5000 cycles are almost the same in diameters, corresponding to electrical connection resistance (Re), also illustrating excellent capacitive behavior of the electrode. The overall resistance (Rt) consisting of electrical connection resistance (Re), electrolyte resistance (Rs), and resistance of ion migration in carbon micropores (Rp) is summarized in Supporting Informatin Table S1.
■
REFERENCES
(1) Shen, W.; Fan, W. Nitrogen-containing porous carbons: synthesis and application. J. Mater. Chem. A 2013, 1, 999. (2) Zhang, L. L.; Zhao, X. S. Carbon-based materials as supercapacitor electrodes. Chem. Soc. Rev. 2009, 38, 2520. (3) Liang, H.; Lee, P. S.; Li, C. Z. 3D carbon based nanostructures for advanced supercapacitors. Energy Environ. Sci. 2013, 6, 41. (4) Wang, D. W.; Li, F.; Yin, L. C.; Lu, X.; Chen, Z. G.; Gentle, I. R.; Lu, G. Q.; Cheng, H. M. Nitrogen-doped carbon monolith for alkaline supercapacitors and understanding nitrogen-induced redox transitions. Chem.Eur. J. 2012, 18, 5345. (5) Zhai, Y. P.; Dou, Y. Q.; Zhao, D. Y.; Fulvio, P. F.; Mayes, R. T.; Dai, S. Carbon materials for chemical capacitive energy storage. Adv. Mater. 2011, 23, 4828. (6) Nishihara, H.; Kyotani, T. Templated nanocarbons for energy storage. Adv. Mater. 2012, 24, 4473. (7) Lee, J.; Kim, J.; Hyeon, T. Recent Progress in the Synthesis of Porous Carbon Materials. Adv. Mater. 2006, 18, 2073. (8) Wang, D. W.; Li, F.; Liu, M.; Lu, G. Q.; Cheng, H. M. 3D aperiodic hierarchical porous graphitic carbon material for high-rate electrochemical capacitive energy storage. Angew. Int. Chem. Ed. 2008, 47, 373.
4. CONCLUSIONS By a simple template carbonization method, nitrogen-doped porous carbons were prepared, in which PAM acts as carbon/ 12030
dx.doi.org/10.1021/ie4017013 | Ind. Eng. Chem. Res. 2013, 52, 12025−12031
Industrial & Engineering Chemistry Research
Article
(9) Xie, K.; Qin, X.; Wang, X.; Wang, Y.; Tao, H.; Wu, Q.; Yang, L.; Hu, Z. Carbon Nanocages as Supercapacitor Electrode Materials. Adv. Mater. 2012, 24, 347. (10) Morishita, T.; Tsumura, T.; Toyoda, M.; Przepiórski, J.; Morawski, A. W.; Konno, H.; Inagaki, M. A review of the control of pore structure in MgO-templated nanoporous carbons. Carbon 2010, 48, 2690. (11) Orikasa, H.; Akahane, T.; Okada, M.; Tong, Y.; Ozaki, J.; Kyotani, T. Electrochemical behavior of carbon nanorod arrays having different graphene orientations and crystallinity. J. Mater. Chem. 2009, 19, 4615. (12) Ruiz-Hitzky, E.; Darder, M.; Fernandes, F. M.; Zatile, E.; Palomares, F. J.; Aranda, P. Supported Graphene from Natural Resources: Easy Preparation and Applications. Adv. Mater. 2011, 23, 5250. (13) Ryoo, R.; Joo, S. H.; Jun, S. Synthesis of Highly Ordered Carbon Molecular Sieves via Template-Mediated Structural Transformation. J. Phys. Chem. B 1999, 103, 7743. (14) Lee, J.; Yoon, S.; Hyeon, T.; Oh, S. M.; Kim, K. B. Synthesis of a new mesoporous carbon and its application to electrochemical doublelayer capacitors. Chem. Commun. 1999, 2177. (15) Itoi, H.; Nishihara, H.; Kogure, T.; Kyotani, T. Threedimensionally arrayed and mutually connected 1.2-nm nanopores for high-performance electric double layer capacitor. J. Am. Chem. Soc. 2011, 133, 1165. (16) Lota, G.; Grzyb, B.; Machnikowska, H.; Machnikowski, J.; Frackowiak, E. Effect of nitrogen in carbon electrode on the supercapacitor performance. Chem. Phys. Lett. 2005, 404, 53. (17) White, R. J.; Antonietti, M.; Titirici, M. M. Naturally inspired nitrogen doped porous carbon. J. Mater. Chem. 2009, 19, 8645. (18) Xu, B.; Hou, S.; Cao, G.; Wu, F.; Yang, Y. Sustainable nitrogendoped porous carbon with high surface areas prepared from gelatin for supercapacitors. J. Mater. Chem. 2012, 22, 19088. (19) Konno, H.; Onishi, H.; Yoshizawa, N.; Azumi, K. MgOtemplated nitrogen-containing carbons derived from different organic compounds for capacitor electrodes. J. Power Sources 2010, 195, 667. (20) Konno, H.; Ito, T.; Ushiro, M.; Fushimi, K.; Azumi, K. High capacitance B/C/N composites for capacitor electrodes synthesized by a simple method. J. Power Sources 2010, 195, 1739. (21) Schwartz, T. J.; van Heiningen, A. R. P.; Wheeler, M. C. Energy densification of levulinic acid by thermal deoxygenation. Green Chem. 2010, 12, 1353. (22) You, B.; Yang, J.; Sun, Y.; Su, Q. Easy synthesis of hollow core, bimodal mesoporous shell carbon nanospheres and their application in supercapacitor. Chem. Commun. 2011, 47, 12364. (23) Yang, G.; Han, H.; Li, T.; Du, C. Synthesis of nitrogen-doped porous graphitic carbons using nano-CaCO3 as template, graphitization catalyst, and activating agent. Carbon 2012, 50, 3753. (24) Wei, S.; Zhang, H.; Huang, Y.; Wang, W.; Xia, Y.; Yu, Z. Pig bone derived hierarchical porous carbon and its enhanced cycling performance of lithium−sulfur batteries. Energy Environ. Sci. 2011, 4, 736. (25) Okpalugo, T. I. T.; Papakonstantinou, P.; Murphy, H.; McLaughlin, J.; Brown, N. M. D. High resolution XPS characterization of chemical functionalised MWCNTs and SWCNTs. Carbon 2005, 43, 153. (26) Ramanathan, T.; Fisher, F. T.; Ruoff, R. S.; Brinson, L. C. Amino-Functionalized Carbon Nanotubes for Binding to Polymers and Biological Systems. Chem. Mater. 2005, 17, 1290. (27) Horikawa, T.; Sakao, N.; Sekida, T.; Hayashi, J.; Do, D. D.; Katoh, M. Preparation of nitrogen-doped porous carbon by ammonia gas treatment and the effects of N-doping on water adsorption. Carbon 2012, 50, 1833. (28) Liu, H.; Zhang, Y.; Li, R. Y.; Sun, X. L.; Désilets, S.; AbouRachid, H.; Jaidann, M.; Lussier, L. S. Structural and morphological control of aligned nitrogen-doped carbon nanotubes. Carbon 2010, 48, 1498.
(29) Datsyuk, V.; Kalyva, M.; Papagelis, K.; Parthenios, J.; Tasis, D.; Siokou, A.; Kallitsis, I.; Galiotis, C. Chemical oxidation of multiwalled carbon nanotubes. Carbon 2008, 46, 833. (30) Pang, H.; Ma, Y.; Li, G.; Chen, J.; Zhang, J.; Zheng, H.; Du, W. Facile synthesis of porous ZnO−NiO composite micropolyhedrons and their application for high power supercapacitor electrode materials. Dalton Trans. 2012, 41, 13284. (31) Zhang, L.; Shi, G. Q. Preparation of Highly Conductive Graphene Hydrogels for Fabricating Supercapacitors with High Rate Capability. J. Phys. Chem. C 2011, 115, 17206. (32) Cao, H.; Xiao, F.; Ching, C. B.; Duan, H. High-Performance Asymmetric Supercapacitor Based on Graphene Hydrogel and Nanostructured MnO2. ACS Appl. Mater. Interfaces 2012, 4, 2801. (33) Kötz, R.; Hahn, M.; Gallay, R. Temperature behavior and impedance fundamentals of supercapacitors. J. Power Sources 2006, 154, 550.
12031
dx.doi.org/10.1021/ie4017013 | Ind. Eng. Chem. Res. 2013, 52, 12025−12031
